Thermionic device and method of evacuating the same



. I I 2 May 17, 1927. R. w. N 6 8,987

THERNIONIC nsvxcm m METHOD or Evwunma wan sm:

Filed Sept. 24. 1920 Pat nted May 17, 1927.

1 UNITED STATES 1,628,987 PATENT OFFICE.

ROBERT W. KING, OF NEW YORK, N. Y.) LSSI GN'OB T WESTERN ELECTRICCOMPANY,

mconrom'run, or NEW Yonx, N.

2., A conrona'rroiw on NEW You 'rnnnmomc mm aunnnrnon or nvncua'rnireTHE slum.

Application filed September 84, 1920. -Serial,No. 412,587. g

electron discharge devices, and pertains more especially to theevacuation of the containing vessels of-suchdevices,

The object of this invention is to obtain quickly and expeditiously ahigh degree of vacuum within the containing vessels ofelectron dischargedevices. This object is attained by removing the occluded gases from theelectrodes by electron bombardment and then cleaning up the gases withinthe vessel by vapzlfzing calcium within the vessel to absorb t e gases.The calcium is preferably suppor d by one of the electrodes and isheated to its vaporiza-f tion temperature by electron bombardment.

In the accompanying drawings Fig. 1 shows a two electrode tube embodyingone form of anode pocket, Fig. 2 shows a three electrode tube embod inga different form of anode pocket, and .ig. 3 shows part of an anodesimilar to that of F i 1 except that a third form of anode poc et isshown in '2 n Fig. 1 the tube 4 comprises envelope 5 of glass-or thelike having the usual inwardly projecting stem 6'from which rises arbor7 of glass or the like. The arbor 7 carries a support8 on which acathode 9 is mounted. The arbor also carries supports (not shown) onwhich anode plate 10 is mounted. Anodeplate 10 carries conductors 11,which support anode plate 12. Le ding in wires for the cathode are shownat 3 and 14. A leadin in wire for the anode is-shown at 15.

ihe cathode which in the form shown is filamentary, is preferably of thetype having a coating of oxldes'of-alkaline earth metals, since thattype has special advanta s in connection with this invention as willpointed out in detail hereinafter. An example'of; such a cathode isdisclosed in United States Patent to Nicolson and Hull'No. 1,209,324,December 19, 1916, electron emitting cathode and the process ofmanufacturing the same.

On the anode plate 12 is a pocket 16 for holding a small piece ofcalcium 17; The side of the pocket is formed by metallic strip .18 inthe form" of a vertical trough, the edges '19 and 20 of the trough beingwelded to anode plate 12.. The bottom of the pocket is "formed by ametallic piece 21, which has a ortion 22 welded to the anode'plate 12and as a portion 23 bent to form a right angle with the portion 22 andcut to the proper shape -to close the bottom end of the trough. In Fig.2 the tube 24 comprises an envelope ,25 or glass or the like having astem 26. The stem carries a metallic collar 27 from which rise anodelates 28 and 29. At their tops the anode p ates carry a metallic box 30con- I taining a blockof lavite 31"from which are supported a doublesurface grid 32 and a cathode filament (not shown), the filament beinglocated between the two grid surfaces. Leading in wires for the filamentare shown at 33' and 34. A leading in wire for the anode is shown at 35and one for the grid is shown at 36. The filament preferably. has acoating such as that referred to in the description of Fi 1.

On the ano eplate 29 is 'a pocket 37 for holding a piece of calcium .17like that referred to in the description of Fig. 1. The

pocket 37 is formed by bowing a square 38 of sheet metal into a shallowdish form and welding the corners of the square tothe plate 29, with oneof the upper edges of the dished square bowed away from the plate 29sufli- 'ciently to permit inserting the calcium in the pocket;

Fig. 3 shows an anode-plate 39 which is like plate 12 of Fig. 1, exceptthat the plate 3.9 has a pocket 40- formed on it by stamping the pocketfrom the plate 39, the pocket opening toward the cathode and having asuitable closure 41 placed over the opening. The closure 41 is ametallic square-held in place by tongues 42 and 43, which being stampedfrom the pocket, afi'ords communication between the. pocket and thevessel. The closure 41 is slid between the tongues and the pocket andpreferably the edges of the closure are welded to the plate 39 at theedges of the pocket. v

In the preferred method of evacuating tubes such, for example, as thosedescribed, the tube is sealed on a suitable pumping apparatus, forinstance, a rotary mechanical pump anda mercury 'aspirator, pumped for11..)

each; (6)- electrically connected for about a 1 minute. This bombardmentis not sufficiently vigorous to vaporize the calcium, but is designed toliberate gas from the plate and the grid. Following this bombardment,the plate and the grid are electricallyoonnected and the plate bombardedby electrons from the cathode vigorously enough to heat the plate sothat the calcium will be vaporized. The pumping of the tube ispreferably continued during all of the foregoing steps. The pressure inthe tube should be low enough before the vigorous bombardment of theanode is started, to insure that the plate -can be heated to thevaporization temperature of, the calcium by the electron bombardmcnt ofthe plate without undue injury to the cathode by bombardment due topositive gas ions. With the alkaline earth oxide coated filamentreferred to above, it is only necessary that the pressure he as low asabout .008 millimeters of mercury. The use of this type of filamentpresents a great 1 advantage in this respect, for, in a poor vacuum thecoated filament is much more active than a tungsten filament, forexample, and therefore, less time is required in the case of the coatedfilaments than in the case of the tungsten filament to pump the tube tothe degree of vacuum necessary before the bombardment for vaporizing thecalcium can be begun. It requires about 3 or 4 minutes of the vigorousbombardment to heat the calcium hot enough to vaporize it. During thistime there-is haze in the tube and the pressure in the tube increases.After the calcium is hot enough to be vaporized, only5 or 6 seconds timeis required to clean up the gases,the haze in the tube disappearing asthe gases are absorbed. If the bombardment is continued after this stagehas been reached, calcium vapor will com I denr-m on the tube walls as ablack deposit,

but will not affect the operation of the tube materially as the vaporpressure of the calcium as well as that (if-the compounds of calciumwith the gases cleaned up is negligibly low.

. Although it has been stated above that in the preferred methodofevacuating tubes the tubes are baked for about 15 minutes afterpumping-has progressed for 3 or 4 minutes, in some instances theevacuation has been satisfactorily carried out without baking, and inother instances of successful evacuation the baking has been done beforeany preliminary pumping. in any case in which the tube-4 are baked, thedurationof the baking may vary considerably from the 15 minute periodreferred to above, depending upon the tube.

In general, the duration of the baking should be longer the greater theamount of energy the tube will be called upon to dissipate during normaloperation.

If instead of using calcium vapor to clean up the gases in the tube,pumping is resorted to, as formerly, for securing the final stage ofevacuation, then instead of requiring but a few minutes of bombardmentto finish the evacuation, about 20 minutes will ordinarily be required.Thus, the use of the calcium effects a great saving in time.

W'hile calcium is the preferred material for use in the anode pocket,other vaporizable material, for example, magnesium, barium. 01'strontium, having low vapor pressure and 'capable of combining with thegases to be removed from the tube to form compounds having negligiblylow vapor pressure at the operating temperature, may

e used in the pocket without departing from the invention.

Although the preferred method of supporting the calcium adjacent theanode is by means of a pocket on the anode, the invention may assumeother aspects. For instance, the anode plates may be made of anickel-calcium alloy containing a small percentage of calcium, or theplates-may be coated with the calcium, without departing from thisinvention.

The tubes shown in Figs. 1 and 2 embody details of construction whichare no part of this invention, the tube of Fig. 1 being claimed in thepatent to H. J. Van DerBijl, U. S. Patent No. 1,479,778, issued January1, 1924, entitled Vacuum tube devices, assigned to the assignee of thisapplication, and the tube of Fig. 2 being claimed in an application ofWilliam F. Hendry, Serial No. 217,565, filed Feb. 16, 1918, entitledElectron discharge devices, assigned to the assignee of thisapplication.

What is claimed is: p

In a vacuum tube, a plate electrode, said plate having a portion struckout to form a pocket, 0. cover for said pocket, tabs cut out from saidplate toengage said cover to' hold it in posltion, and vaporizablemate-' rial contained within said pocket.

In witness whereof, I hereunto subscribe my name this 20th day ofSeptember, A. D.

ROBERT W. KING.

